Autism Linked with Air-Pollution Exposure During Pregnancy

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Pregnant women who are exposed to high levels of air pollution
may be more likely to give birth to children with autism,
according to a new study.

The researchers found that the pregnant women in the study who
lived in the most-polluted areas were up to two times more likely
to have a child with an autism spectrum disorder (ASD), compared
with those who lived in the least-polluted areas.

The air pollutants linked to autism included diesel fuel, lead,
manganese and mercury. For most pollutants that the researchers
studied, associations with autism were stronger in boys than in
girls.

The results add to evidence found in
previous studies suggesting that air pollution might be a
risk factor for autism.

It is not clear how heavy metals or other chemicals found in air
pollution may affect a developing fetus, but studies have shown
traffic-related pollutants, such as diesel, can induce
inflammation of the brain in animals, the researchers said.

"Our results suggest that new studies should begin the process of
measuring metals and other pollutants in the blood of pregnant
women or newborn children to provide stronger evidence that
specific pollutants increase risk of autism," said study
researcher Marc Weisskopf, associate professor of environmental
and occupational epidemiology at Harvard School of Public Health.

In the study, the researchers looked at 325 women who had a child
with autism and 22,000 women who had a child without autism.
Using air-pollution
data from the U.S. Environmental Protection Agency, the
researchers estimated levels of pollutants at the time and place
of each child's birth.

The results showed that women living in areas with the highest
levels of diesel or mercury in the air were twice as likely to
have a child with ASD, compared with those living in the areas
with the lowest levels.

Women who were exposed to other types of air pollution — such as
lead, manganese and methylene chloride — were about 50 percent
more likely to have a child with ASD than women who lived in the
areas with the lowest concentrations of these pollutants.

The results held after adjusting for other possible ASD risk
factors, such as parents' income, education and smoking
during pregnancy. However, the findings show a link — not a
cause-and-effect relationship — between autism and pollution, the
researchers said. More work is needed to confirm the results.

There were 279 boys and 46 girls with ASD in the study. While the
link with pollution seemed stronger for boys compared with girls,
the researchers noted there were few girls with autism in the
study, and said the finding should be examined further.

Another explanation for the gender difference in the results is
that boys may have a generally greater vulnerability to ASD, the
researchers said. The toxic effects of air pollutant may impact
boys' development more easily or profoundly, resulting in
autism, they said.

The study was published today (June 18) in the
journal Environmental Health Perspectives.